1. Field of the Invention
This invention relates generally to document handling systems, and more particularly, to the control of entrance transport element pinch force on documents of various lengths.
2. Discussion
Document handling systems, such as check processors, tag printers and ticket printers, are used to process a variety of documents at high speeds. FIG. 1 illustrates a conventional system used in a document handling system for stopping a document in a high speed transport so it can be printed on with a printer. As shown, the conventional system typically includes an entrance transport element 12 having a drive roller element 14 and a corresponding pinch roller element 16. The system also includes a capstan element 18, a pinch roller element 20 corresponding to the capstan element 18, an edge sensor 22, a hammer bank 24, a print drum 26, a ribbon 28, and an exit transport element 30. The exit transport element includes a drive roller element 32 and a corresponding pinch roller element 34. In the example shown, MICR amount fields are being printed on a check 10.
Documents come in a variety of weights and lengths. For example, in check processing, the document lengths range from about 5 inches to 9 inches. FIG. 1 illustrates the case of a relatively short document 10. In particular, FIG. 1a shows a document 10 moving toward a print station. As shown, the entrance drive element 14 and pinch roller element 16 are in contact with the document 10. Typically, a document 10 is moved at high speed up to a print station by the entrance transport element 12. When the document 10 is in the grip of the capstan element 18 only, the capstan element 18, and hence the document 10, is decelerated to the desired stop position, shown in FIG. 1b. For precise positioning, the leading edge 10a of the document is sensed by the edge sensor 22. The edge sensor 22 is a known distance from the desired stop position. The motion of the capstan element 18 is controlled by a single motor (not shown) which is part of a servo loop.
After printing, the document 10 is accelerated up to the speed of the exit transport element 30 by the capstan element 18. The exit transport element 30, usually running at high, constant speed, moves the document 10 to other devices for further processing shown in FIG. 1c. 
As is conventionally known, each of the pinch roller elements 16, 20 and 34 are normally spring loaded against the entrance 12 and exit 30 drive roller elements and against the capstan element 18, respectively, in order to provide drive force for the document. A pinch force Fp is generated by the interaction of the drive roller element 14 or 32 or capstan element 18 and the respective pinch roller element. The pinch force Fp is applied to the document 10 generally perpendicular to the path of travel.
If the document 10 is short enough, it will not be under the influence of the entrance transport element 12 while the capstan element 18 is decelerating it and holding it in the print position.
However, because some document processing, such as check processing, requires that multiple documents of varying length be processed, reliable document transporting dictates that at least one drive or capstan roller element be contacting the document at all times. As such, drive roller and capstan element spacing needs to be small to reliably transport short documents. Unfortunately, this results in long documents being under the influence of a drive roller and capstan element for a greater period of time, which has an undesirable effect on document handling apparatus performance.
FIG. 2 illustrates printing on a relatively long document 10xe2x80x2 using conventional methods. As best shown in FIG. 2b, a long document 10xe2x80x2 is under the influence of the entrance transport element 12 when the capstan element 18 is decelerating and attempting to maintain the document position during printing. To keep the document 10xe2x80x2 from buckling, from slipping forward during deceleration, and to help the capstan element 18 hold the document 10xe2x80x2 in position, the small pinch forces Fp are typically used at the entrance transport element 12 to allow the drive roller element 14 to slip. Unfortunately, this action usually compromises document transport reliability since there is still some force on the document due to the friction between the document 10xe2x80x2 and the entrance drive roller 14 when the document 10xe2x80x2 is being driven by 12 with low drive force during its approach to the print station.
It is an thus object of the present invention to provide shorter stopping and starting times to improve throughput in document processing equipment.
Another object of the present invention is to remove the entrance transport pinch force during document deceleration and stop during document processing, and then return the pinch force just after processing is completed and the document is delivered to the exit transport.
The present invention is directed to an apparatus for providing pinch force control to the entrance transport element in a document handling system. The document handling system includes an entrance transport element comprising a drive roller element and a pinch roller element. A pinch force relief mechanism is coupled to the pinch roller element and is positionable between a pinch force mode and a non-pinch force mode. The apparatus also includes a control element adapted to control actuation of the pinch force relief mechanism between the pinch force mode and the non-pinch force mode. When the control element places the pinch force relief mechanism in the pinch force mode, the pinch roller element is positioned such that a pinch force is exerted on a document. Conversely, when the control element places the pinch force relief mechanism in the non-pinch force mode, the pinch roller element is positioned such that no pinch force is exerted on the document.
Accordingly, depending upon document length, the pinch force is automatically removed from entrance transport element, preventing external forces from affecting the positioning of the document.
Furthermore, a dashpot may be added to better control motion of the pinch force relief mechanism.